Construction machines, such as hydraulic excavators and hydraulic cranes, perform various work by means of a hydraulic drive system. For example, Patent Literature 1 discloses a hydraulic drive system in which hydraulic oil is supplied from a variable displacement pump to a turning motor via a turning control valve.
To be specific, in the hydraulic drive system disclosed in Patent Literature 1, the turning motor is connected to the turning control valve by a pair of supply/discharge lines. The turning control valve includes a pair of pilot ports that are connected to a turning operation device by a pair of pilot lines. The turning operation device is a pilot operation valve that outputs a pilot pressure corresponding to the inclination angle of an operating lever to the turning control valve.
The tilting angle of the pump is adjusted by a flow rate adjuster (in Patent Literature 1, a regulator 15a). The flow rate adjuster is controlled by a controller, such that the tilting angle of the pump increases in accordance with increase in the pilot pressure outputted from the turning operation valve.